Installation for simultaneously drying pulverising and grading granular materials



3,512,723 SING May 19, 1970 J. A. GEOFFROY INSTALLATION FORSIMULTANEOUSLY DRYING PULVERI AND GRADING GRANULAR MATERIALS 5Sheets-Sheet 1 Filed June 26, 1968 kin. tJ racts May 19, 1970 J. A.sEoFFhoY 3 512,723

9 INSTALLATION FOR SIMULTANEOUSLY DRYING PULVERISING AND GRADINGGRANULAR MATERIALS Filed June 26, 1968 3, Sheets-Sheet 2 M y-19, 1910 JA. GEQFFROY 3,512,723

INSTALLATION FOR SIMULTANEOUSLY DRYING PULVERISING AND GRADING GRANULARMATERIALS Filed June 26, 1968 3 Sheets-Sheet 5 United States Patent 4int. c1. B02: 13/134, 13/288, 21/00 U.S. Cl. 241-34 8 Claims ABSTRACT OFTHE DISCLOSURE Improved installation for simultaneously pulverizing in afluidized bed, grading and drying or preheating nonagglutinant granularmaterials at the temperature of the drying or preheating treatment,wherein the chamber connected to a lower combustion chamber and to anupper dust removing cyclones comprises in an upward direction:

A zone for homogenising the flow of hot gases issuing from thecombustion chamber,

A drying zone wherein the product to be treated is introduced,

A pulverising zone wherein the product formed a fluidized layer and issubjected to the impact of a pulverisor, and

A gravity grading zone.

The present invention relates to an improved apparatus forsimultaneously pulverising, grading and drying or preheatingnon-agglutinant granular materials at the drying or preheatingtemperature.

It is known that simultaneous pulverising, grading and drying orpreheating operations on non-agglutinant materials can easily be carriedout in a fluidisation reactor having an impact pulverisor, for example acage type pulverisor, partially or totally immersed in a fluidised layerof the material to be treated.

In a known apparatus, the fluid layer is fed with material to be treatedby pneumatic transport of the material by means of hot gases arriving inthe fluidised layer beneath the moving portion of the cage typepulverisor. Such a device is described in the French Pat. No. 1,357,803.

An advantage of this device is that gases at temperatures higher thanthose occurring in a conventional drying or preheating in a fluidisedbed can be used and this enables the contact time of the very fineproducts with the gases which propel them to be reduced.

In order to encourage the introduction of the materials to be pulverisedinto the interior of the movable portion of the pulverisor, it has beenproposed to divide this portion into several cages placed side by sideon a single shaft and separated by a clear space, a deflector assemblyif necessary directing the products to be pulverised towards theinteriors of cages adjacent to the deflector assembly. Such a device isdescribed in French IPat. No. 1,444,902 corresponding to US. Pat. No.3,381,901.

The present invention concerns an improved installation forsimultaneously pulverising in a fluidised bed, grading and drying orreheating non-agglutinant granular materials at the temperature of thedrying or preheating treatment, essentially characterised in that itcomprises in combination:

Means to produce a constant flow of hot gases;

A fluidisation chamber of rectangular section having a pyramidal basewhich is upwardly diverging and of section such that the materials to'be pulverised form a fluidised suspension therein;

ice

A vertical hot gas inlet conduit connected to the base of thefluidisation chamber, the section of the conduit being smaller than thatof the fluidisation chamber and composed of two portions connected by aconvergent-divergent portion;

Means for feeding the material to be pulverised leading into thevertical hot gas inlet conduit between the convergent-divergent portionand the base of the vertical fluidisation chamber;

A horizontally disposed pulzerisor having hammers and being locatedwithin the zone of the vertical fluidisation chamber where the productsform a fluidised suspension;

An evacuation conduit connected to the upper part of the verticalfluidisation chamber and leading into a pneumatic transport duct;

A dust removing installation having suction cyclones, cognected to theoutlet of the pneumatic transport duct; an

means for maintaining the temperature of the fluidised layer at aconstant value.

In accordance with other characteristics of the invention, combinationsof which can be used:

The hammers of the pulverisor are constituted by bars of constantthickness;

The feed means for the material to be pulverised are constituted by aband screw in which the width of the band increases in the direction ofmovement of the materials;

The evacuation conduit is provided at its base with a connectingelement, the section of which converges in an upward vertical direction;

The height of the base of the connecting element of the evacuationconduit with respect to the fluidised bed is adjustable;

The means for producing a constant flow of hot gases are constituted inknown manner by a combustion cham her in which a fuel is burned underneutral combustion;

The means for maintaining the temperature of the fluidised layer at aconstant value are constituted by a variable speed motor driving thefeed screw for the material to be pulverised, a temperature sensingdevice immersed in the fluidised layer and a device known per se forcausing the rotational speed of the motor driving the feed screw to bevaried according to the temperature variation in the fluidised layer.

In an alternative embodiment, the means for maintaining the fluidisedlayer at a constant temperature are constituted by a temperature sensingdevice immersed in the fluidised layer and a device known per se tocause the flow of fuel to vary inversely as the temperature of thefluidised layer.

Other characteristics and advantages of the present invention willappear from the following description with reference to the accompanyingdrawings, in which:

FIG. 1 is a general view of the installation of the invention;

FIG. 2 is a sectional view to a larger scale of the zone in whichpulverisation, drying and grading proper of the materials to be treatedare carried out;

FIGS. 3 and 4 are two detail views showing the movable portion of thehammer pulverisor in vertical and horizontal section respectively; and

FIG. 5 is a view in partial section of the stufling box installed ateach end of the shaft driving said movable portion.

The installation of the present invention shown by way of example in thedrawings comprises a vertical chamber of rectangular transverse sectiondesignated by the general reference 1, which chamber is connected at itslower portion to a combustion chamber 2 and, at its upper portion, to adust removing installation having cyclones 3 and 4.

Considering the vertical chamber 1 in an upward direction, four zonescan be distinguished:

(a) A zone 5 for homogenising the flow of hot gases issuing from thecombustion chamber 2 having the shape, at its upper portion, of aconverging-diverging neck 6 whose outlet section is smaller than theinlet section so as to increase the speed at which the hot fumes rise.

(b) A drying zone 7 through which the products to be pulverised, storedin the hopper 8 and introduced at the bottom of the drying zone by meansof a conveyor screw 9, are transported pneumatically.

(c) A pulverising zone 10 whose transverse section is greater than thetransverse section of the drying zone 7 such that, as the speed of thegases decreases therein, the mass of products to be pulverised propelledby the gases assumes the form of a fluidised layer 11. The movableportion 12 of an impact pulverisor, described hereinafter, is installedin the fluidised layer 11.

((1) Finally, a gravity grading zone 13 having a section equal to thatof the pulverising zone 10.

The operation of the installation will be better understood by referringmore particularly to FIG. 2 and to the following description of the pathfollowed by the products to be pulverised. The products stored in thehopper 8 are introduced at the base of the drying zone 7 by means of theconveyor screw 9. Since the products to be pulverised are damp and thusclinging together, the conveyor screw is preferably a band screw, thewidth of the band increasing in the direction of flow of the products.This type of conveyor screw is described in French Pat. No. 1,483,954corresponding to US. application Ser. No. 641,900 filed May 29, 1967,and now abandoned. It enables the products to be pulverised to becontinuously extracted over the whole length of the base of the hopper8, whilst at the same time avoiding the formation of curved cavitieswithin the hopper and preventing the products from sticking to thewalls.

The products to be pulverised are propelled and predried by the risingcurrent of hot gases.

The speed of the gases decreases in the pulverising zone 10 because ofthe widening of the conduit, and the mass of products to be pulverisedforms a fluidised layer 11 if the ratio of the flow of gases to thesection of the conduit in the pulverising zone is calculated as afunction of the granulometry of the products to be pulverised.

The movable part of a hammer pulverisor 12, rotatably driven by means ofa motor 14 and driving chain 15, is completely immersed in the fluidisedlayer. In this layer the drying of the products to be pulverised iscompleted and the products are pulverised by the hammers 16 betweenwhich they penetrate.

In order to encourage penetration of the products to be pulverisedbetween the hammers 16 and thus avoid seizing of the installation byaccumulation of products under the movable part of the pulverisor, thehammers 16 are preferably constituted by simple bars of uniformrectangular transverse section as shown in FIGS. 3 and 4.

The driving shaft 17 of the movable part of the pulverisor is mounted bymeans of a known system of bearings and air swept stufiing boxes (FIG.5) in order to protect the seals 18 from contact with atmospheric dustand to prevent rapid wear of the seals and of the shaft 17 in thevicinity of the bearings.

The zone of the vertical chamber 1 located above the fluidised bed isconnected to the transport duct 19, leading to the dust removinginstallation, by means of a conduit 20 having at its lower portion aconnecting element 21 which converges in the upward vertical direction.The grading zone 13 is defined by the upper level of the fluidised layer11 and the base of the connecting element 21.

In this zone, the non-pulverised or insufiiciently pulverised particlesin the fluidised layer 11 and propelled by the gases leaving thefluidised layer separate out and fall back into the fluidised layer 11where they are subjected to additional pulverisation, while the driedand pulverised particles which have attained the desired fineness arepropelled pneumatically through the transport duct 19.

In order to produce eflicient grading, taking into account the spec dofthe gases, it is necessary for the rising gases to travel, above thefluidised layer, through a height, known as the return height, which issufficiently great for a regular rate to encourage grading.

Expressed differently, the return height, i.e. the vertical distance Hseparating the upper level of the fluidised layer from the base of theconnecting element 21, must be large enough to allow the largeparticles, ejected from the bed and whose speed of fall in the risinggases is greater than the speed of rise of the gases, to fall back.

Since the return height H to be provided is principally in proportion tothe granulometry to be achieved, the optimum height of the grading zone13 is adjusted experimentally by altering the height of the lower end ofthe connecting element 21 with respect to the upper level of thefluidised layer, for example by altering the length of the conduit 20.

The pneumatic transport duct 19 takes the mixture of the gases and thedried and sufliciently pulverised products to the dust removinginstallation which has a first cyclone 3 and second cyclone 4. Theparticles trapped by the two cyclones are led to their place of use byany known means which are not shown.

Since the gas producing power of the fuel burning under neutralcombustion is almost equal to its combustive power, the quantity of hotcombustion gases leaving the combustion chamber 2 may be regarded asconstant, whatever may be the amount of fuel used.

There are two possible methods of regulating the temperature of thefluidised bed:

1) The temperature of the combustion gases leaving the combustionchamber is maintained at a constant value by adjusting once and for allthe amount of fuel as a function of the quantity of gases to be producedand thus of the quantity of combustive air, and the rate of introductionof the products to be pulverised is adjusted as a direct function of thetemperature of the fluidised layer.

The apparatus in this case comprises a temperature sensing device 22immersed in the fluidised layer 11, and a regulating device 23, knownper se, causing the speed of rotation of the motor 24 driving the screw9 to be varied in the same sense as the observed temperature variation.

(2) The rate of introduction of the products to be pulverised ismaintained at a constant value and the temperature of the gases isadjusted as an inverse function of the temperature of the fluidisedlayer.

In this case, the apparatus comprises a temperature sensing device 22immersed in the fluidised layer, and a regulating device 25, of anyknown type, acting on a valve 26 in such a manner that the amount offuel flowing increases when the temperature of the fluidised layer 11fal s and vice-versa.

The fact that a hammer pulverisor is used'lessens the risk of theproducts to be pulverised accumulating beneath the movable portion ofthe pulverisor, such accumulation occurring in a Carr pulverisor due tothe difliculty experienced by the products to be pulverised inpenetrating within the case thereof through the bars.

Moreover, the replacement of worn elements on the movable part of thepulverisor (notably the hammers) is an easyoperation not requiringprolonged halting of the installation.

The apparatus of the invention was used to pulverise coal granuleshaving the characteristics shown in the first line of the followingtable.

W J Granulometry Humidity mm. 3.15 mm. 2mm. 1mm. 0.5 mm. 0.2 mm. 0.1 mm.

Before ulverisation perce t 4. 4 100 93. 1 78 57. 1 35 20. 1 7. 6 Afterulverisation perc nt 1.1 100 98. 2 91. 7 78. 2 62 45. 7 25. 6

The installation operated for three hours with a flow (g) an evacuationconduit having a section smaller of coal of9t./h. 10 than that of thevertical fluidisation chamber and The temperature of the gases was 360C. and the temperature of the fluidised layer was maintained at Thepulverising and grading zone had the following dimensions: 0.49 m. X 1m. and the movable part of the pulverisor had a diameter of 0.90 m. Thespeed under no load of the fumes in the pulverising zone was 3.6 m./s.

The return height H was 2 m.

The average characteristics of the 27 t. of pulverised and dried coalare shown in the second line of the above table.

The treatment required an average hourly consumption of electricalenergy of 17 kwh., or l7/9=1.9 kwh. per ton of pulverised and driedcoal.

summarising, the main advantages of the insta lation of the presentinvention are:

Great regularity of operation,

Easily realisable automation,

Ease of service and maintenance,

And above all, low electrical energy consumption compared with knowndevices to achieve comparable granulometries.

It is clear that modifications of detail can be made to the installationof the invention without departing from the scope of the invention.

What is claimed is:

1. An improved installation for simultaneously pulverising in afluidised bed, grading and drying or preheating nonagglutinant granularmaterials at the temperature of the drying or preheating treatment,comprising from bottom to top:

(a) means for producing a substantially constant flow of hot gaseousfluid;

(b) a vertical conduit for ensuring the circulation of said hot gaseousfluid, composed of two parts corinected together by aconvergent-divergent portion;

(c) means for feeding the material to be pulverised leading into saidvertical hot gaseous fluid circulation conduit above saidconvergent-divergent portion;

(d) a vertical fluidisation chamber of substantially uniform rectangularsection having a base in the form of a pyramid diverging in an upwarddirection and connected at its lower part to the top of said verticalhot gaseous fluid circulation conduit;

(e) the outlet section of said pyramidal base is greater than thesection of said vertical hot gaseous fluid circulation conduit andcauses the materials to be pulverised to form a fluidised suspension insaid vertical fluidisation chamber;

(f) a horizontally disposed pulverisor having hammers and being locatedin the lower part of the vertical fluidisation chamber;

connected to the upper part of said chamber;

(h) and means for maintaining the temperature of the fluidised layersubstantially constant.

2. An installation according to claim 1 wherein the pulverising hammersare constituted by bars of unif rm thickness.

3. An installation according to claim 1 wherein the means for feedingthe material to be pulverised is constituted by a band screw, the Widthof the band of which increases in the direction of movement of thematerial.

4. An installation according to claim 1 wherein the evacuation conduitis provided at its base with a connecting element whose sectionconverges in an upward vertical direction and which connects theevacuation conduit to the vertical fluidisation chamber.

5. An installation according to claim 4 in which the height of the baseof the evacuation conduit connecting element with respect to thefluidised bed is adjustable.

6. An installation according to claim 1 in which the means for producinga substantially constant flow of hot gaseous fluid is constituted by acombustion chamber in which a fuel is burned by neutral combustion.

7. An installation according to claim .1 wherein the means formaintaining the temperature of the fluidised layer at a substantiallyconstant value is constituted by a variable speed motor driving themeans for feeding the material to be pulverised, by a temperaturesensing device immersed in the fluidised layer and by a device forcausing the speed of rotation of said motor to vary as a direct functionof temperature variations in the fluidised layer.

8. An installation according to claim 1 wherein the means formaintaining the temperature of the fluidised layer at a substantiallyconstant value is constituted by a temperature sensing device immersedin the fluidised layer and by a device for causing the fuel flow to varyinversely as temperature variations in the fluidised layer.

References Cited UNITED STATES PATENTS 1,814,560 7/1931 Kreisinger241-59 X 1,875,817 9/1932 London 241-58 2,075,506 3/1937 Crites 24l--188X 3,050,018 8/1962 Pearson.

FOREIGN PATENTS 1,357,803 3/1964 France.

1,483,954 3/1967 France.

ROBERT C. RIORDON, Primary Examiner D. G. KELLY, Assistant Examiner US.Cl. X.R. 241-62 Dedication 3,512,723.Jaciues A. Geoffrey, Forbach,France. INSTALLATION FOR SIMU TANEOUSLY DRYING PULVERISING AND GRAD- INGGRANULAR MATERIALS. Patent dated May 19, 1970. Dedication filed Dec. 20,1979, by the assignee, Oharbomwges De France.

Hereby dedicates to the Public the remaining term of said patent.

[Ofi'icial Gazette, M arch 4, 1980.]

